A mid-level developer is responsible for the quality of their code. Testing is the only way to prove that quality exists.
1The Red-Green-Refactor Loop
Test-Driven Development (TDD) flips the script: Write the test first (Red), write just enough code to pass (Green), then clean it up (Refactor). This ensures 100% coverage and clean design.
2Integration vs. E2E
Integration tests check how components work together. E2E tests check how the whole system works together. Mid-level devs know that E2E is for 'Critical Paths' (like Login or Checkout), not for every single button click.
3Continuous Integration (CI)
Tests shouldn't just run on your machine. They should run automatically on every Pull Request. This 'CI' pipeline is the guardian of the production environment, blocking bad code from ever being deployed.
